Genetic recombination is a process in which information from one DNA molecule is transferred to a second DNA molecule. In E. coli it is essential for the repair of damaged DNA and the maintenance of cell viability. Although the phenomenon has been studied genetically for years, its molecular mechanism is poorly understood. Since the genetic analysis of recombination is well defined in E. coli, this organism will be utilized to try and unravel the sequence of enzymatic events involved in this process. recB and/or recC mutations are indirectly suppressed in the absence of exonuclease I. By studying the homogeneous enzyme and temperature sensitive indirect suppressor mutations (sbcB and xonA), it is hoped that the in vivo role of this enzyme can be established. recB- and/or recC- alleles can also be indirectly suppressed by a second type of mutation called sbcA-. In these strains a new ATP-independent double- stranded exonuclease (exonuclease VIII) appears. The precise substrate specificity of homogenous exonuclease VIII will be determined in order to assess its role in genetic recombination. The temperature sensitive enzymes produced by recB270 and/or recC271 (exonuclase V) will be purified to homogeneity and their catalytic function analyzed. The in vitro suppression of temperature sensitivity by high ATP levels will be studied to determine the precise role of the recB-recC gene products in vivo. Isolation and characterization of the gene products associated with recA, recF, recJ, recK and recL will be attempted by employing specialized affinity chromatographic procedures on strains carrying these mutations in a background deficient in exonucleases I, III and V.